Vermiculite ore is comprised of individual magnesium aluminum silicate lamellae bonded together by divalent metal cations, mostly magnesium. Each lamella is a layer of magnesium aluminum silicate having a thickness of about 9.25 angstroms.
In the prior art, aqueous suspensions of discrete vermiculite platelets, each platelet several lamellae thick, have been made by several methods, as for example, by contacting vermiculite ore with an aqueous solution of at least one salt of sodium, lithium, or an organo-substituted ammonium cation, followed by aqueous washing, so that the ore swells to at least twice its original volume, and shearing the swollen ore into the discrete platelets. Such discrete platelets are commonly referred to as chemically delaminated vermiculite platelets. Films and coatings cast from such suspensions have good flame resistant properties, but poor stability in water.
Various methods for improving the water stability of vermiculite structures is taught in the prior art. These include the incorporation of organic polymers and copolymers; soaking the structure in solutions of divalent metal cations; incorporation of silicone polymer precursors; or contacting the finished structure with the vapor of certain amines or ammonia gas.
Unfortunately, the processes for improving the water stability of solid objects made from suspensions of vermiculite platelets have not been entirely satisfactory. Many of the aforementioned processes are not satisfactory because they involve tedious post treatments, or require the incorporation of large quantities of organic materials which degrade the high temperature properties of the structures.